Electrical resistor



June 12, 1934. Q Q w M 1,962,673

ELECTRICAL RESISTOR Filed Nov. 24, 1930 2 Sheets-Sheet l ATTORNEY 2Sheets-Sheet 2 INVENTOR BY wv ATTORNEY G. O. WILMS ELECTRICAL RES ISTORFiled Nov. 24, 1930 Guszav U: Wums June 12, 1-934.

Patented June 12, 1934 UNITED STATES PATENT OFFICE ELECTRICAL RESISTORGustav 0. Wilms, Milwaukee, Wis., assignor, by mesne assignments, toAllen-Bradley Company, Milwaukee, Wis., a corporation of Wisconsin Thisinvention relates to certain new and useful improvements in electricalresistors and particularly to fixed resistance units used with motorcontrol apparatus.

Heretofore units of this type consisted of grids of cast iron or othermetal having the desired degree of ohmic resistance, but thisconstruction was costly and objectionable in that it resulted in acumbersome and bulky unit very susceptible to breakage and lacking inflexibility of installation. Such cast grids were also objectionable fortheir lack of proper radiation.

The shortcomings of resistors of this type were recognized and attempts.have been made to overcome these objections, but all devices so farproposed have been entirely too costly.

It is therefore an object of this invention to provide a durable andeconomically manufactured electrical resistor suitable for the purposestated.

A further object of this invention is to re duce the cost of resistorsof the character described by forming them entirely of sheet metal.

Another object of this invention is to provide a resistor of thecharacter described which has a large radiating surface to eflicientlydissipate heat incidental to the passage of current therethrough.

Another object of this invention is to provide a resistance unit of thecharacter described which is flat to facilitate stacking of a number ofunits to be connected in series or in parallel.

A further object of this invention is to provide a resistor of thecharacter described which has convenient means for attaching conductorsat any portion thereof, formed integral therewith.

And another object of this invention resides in the method ofconstructing or forming electrical resistors of strips of sheet metal.

With the above and other objects in view which will appear as thedescription proceeds, my invention resides in the novel construction,combination and arrangement of parts substantially as hereinafterdescribed and more particularly defined by the appended claim, it beingunderstood that such changes in the precise embodiment of theherein-disclosed inven- 50 tion may be made as come within the scope ofthe claim. v

In the accompanying drawings, I have illustrated one complete example ofthe physical embodiment of my invention constructed ac- 56 cording tothe best mode I have so far devised for the practical application of theprinciples thereof, and in which:

Figure 1 is a plan view of an electrical resistance unit constructed inaccordance with my invention;

Figure 2 is a side view of the unit illustrated in Figure 1;

Figure 3 is a transverse sectional view taken through Figure 1 on theplane of the line 3-3;

Figure 4 is a side view of a block of re- 5 sistance units shown inFigure 1 illustrating the manner of stacking them;

Figure 5 is an end view of the structure shown in Figure 4; and

Figure 6 is a fragmentary, perspective view illustrating a strip ofsheet metal showing its appearance after it is punched and before it isformed into the finished resistance unit.

Referring now more particularly to the accompanying drawings, it is seenthat the resistor, designated generally by the numeral 6 is formedentirely of sheet metal. In forming the resistor, a strip of sheet metal7, see Figure 6, is cut as at 8 alternately from opposite sides todivide the strip into a plurality of sections 89 9 connected alternatelyat opposite ends. The intermediate portions of the sections 9 arepressed alternately downwardly and upwardly to permit a pair of mountingrods 10 to be woven therebetween, as illustrated in Figure 1. The rods10 have insulating sleeves 11 extending throughout substantially theirlength to electrically insulate the sections 9 therefrom, and the endsof the rods are threaded to receive nuts 12.

After the mounting rods 10 are interwoven 90 between the oppositelydirected sections 9, the intermediate portions of the sections arepressed down over the rods, as at 13, see Figure 3, to secure the rodsagainst shifting, but it is noted that suflicient space is left betweenthe adjacent edges of the sections to provide electrical clearance. Theendmost sections 9 are folded over the adjacent rods 10 and riveted inplace as at 14.

The metal 15 at the ends of the sections 9 between the cuts 8 and bywhich adjacent sections are connected, provides a terminal for eachsection, and to facilitate the attachment of conductor wires thereto,apertures 16 are formed therein. Preferably the terminals or connectingportions 15 are twisted at an angle to the longitudinal axis of theunit, as best shown in Figure 2, to insure sufficient electricalclearance therebetween. The sections 9 thus form a zigzagging currentpath between the ends of the unit or between any two spaced terminalmembers 15.

The slots 8 may be cut into the blank sheet in any desired manner and avery simple and eflicient method is to feed the blank, as a strip, to apunch press or other suitable machine having means for cutting theslots. The material may be unreeled from a roll as it is fed to thepress, so that a continuous manufacturing operation is possible andwasting of material preeluded.

Punched or slotted strips of materials having different degrees of ohmicresistance may be carried on hand and in this manner units of anypractical resistance requirements may be quickly and economicallymanufactured by merely cutting the slotted strips to the necessarylengths and mounting the cut lengths on the supporting rods in themanner hereinbeiore described.

This construction, as will be readily apparent, has numerous advantagesover the grid structures heretofore used as resistors in motor controlapparatus, as it provides a substantial and nonbreakable unit of smalldimensions, and the fact that it is formed entirely of sheet metal givesit a large capacity for heat radiation. It is also possible with thisunit to obtain a relatively high degree of resistance in a comparativelysmall space, and by the use of different materials various degrees ofohmic resistance may be had without changing the over-all physicaldimensions of the unit.

The fact that the unit is fiat greatly facilitates stacking or combininga number of individual units in a single structure and in Figures 4 and5 one method of combining or stacking a means number of units isillustrated. As herein shown, the ends'of the mounting rods 10 arepassed through suitable apertures formed in end plates or supports 17and by means of the nuts 12 are secured thereto.

With this arrangement, connection of the units in series or in parallelis a simple matter and in Figure 4, conductors 18 are shown connectingthe units in series.

From the foregoing description taken in connection with the accompanyingdrawings, it will be readily apparent to those skilled in the art towhich an invention of the character described appertains, that I providea novel and extremely simple electrical resistor particularly adaptedfor use with motor control apparatus which may be easily manufactured ata low cost, is substantial and nonbreakable, and has numerous advantagesnot found in resistors heretofore proposed for this purpose.

What I claim as my invention is:

An electrical resistor comprising, a sheet of metal having the desiredohmic resistance and having cuts extending partially therethroughalternately from opposite sides to provide a plurality of adjacentsections connected alternately at opposite ends, supporting rodsextending transversely across the sections and disposed in said cuts,tubular rigid self-supporting insulators on the rods to electricallyspace the intermediate portions of adjacent sections, and the connectingend portions having apertures to afford terminal means for theattachment of external conductors at different points in the length ofthe unit.

GUSTAV O. WILMS.

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